The present disclosure relates to conveyance devices in which a developer is conveyed, development devices including such a conveyance device, and image forming apparatuses including such a development device.
A development device circulates and conveys a developer between a first conveyance path and a second conveyance path which are provided in a development housing. The developer is conveyed in the first and second conveyance paths by respective stirring screws provided in the first and second conveyance paths. A conveyance direction in the first conveyance path is opposite to a conveyance direction of the second conveyance path. The stirring screws of the development devices each include a shaft portion, and a plurality of helical parts which are joined successively around the shaft portion. The developer is conveyed in the conveyance direction by the stirring screws being driven to rotate in the development housing.
If the adhesiveness of the developer increases due to degradation of the developer, the developer may adhere to the shaft portion of the stirring screw. If the developer adheres to the shaft portion, the shaft portion, in effect, has a larger thickness. As a result, the conveyance performance of the stirring screw decreases. A type of stirring screw does not include a shaft portion at a middle portion in the axial direction. In other words, such a stirring screw has a hollow shape.
Compared to the stirring screw including the shaft portion extending in the axial direction, the stirring screw having the hollow shape tends to have lower performance in terms of conveyance of the developer in the axial direction. A means for detecting the amount of the developer may be provided in a region which is located on a downstream side of the first conveyance path in which the stirring screw having the hollow shape is provided, and faces a communication path between the first and second conveyance paths. The developer amount detecting means detects the amount of the developer in the first conveyance path. The developer amount detecting means includes an eddy current sensor etc. The eddy current sensor outputs a voltage value which varies depending on the amount of the developer which is conveyed in the communication path while facing the eddy current sensor. The amount of the developer in the first conveyance path is detected based on the voltage value.